The present invention concerns the field of pipelines, used in production offshore or at sea, for the conveyance of fluids and, in particular, hydrocarbons. More specifically, it concerns the connecting device between a riser linking a subsea installation located on the seabed to an intermediate surface or subsurface installation such as a buoy and a jumper designed to link the top end of said riser to a production and/or storage facility located at the surface. It also concerns the configuration of the associated riser comprising all the lines and connecting devices linking the subsea installation (wellhead manifold for example) to the surface production facility.
Many riser configurations designed to link a subsea installation to a surface facility are known in the prior art. For example, we can cite not only configurations of catenary risers, the latter comprising either flexible or rigid lines, but also configurations featuring vertical risers. In these latter cases, the configuration is usually in form of a flow-line pipe linked to a vertical riser by a bottom connecting device (such as the one illustrated in patent WO 02/103153). The top end of the riser is connected to a second line, most often flexible and generally shorter, called a “jumper”. This line extends the riser to allow the conveyed fluid to flow towards a production and/or storage facility usually at the surface. The bottom end of the vertical riser is anchored at the bottom connecting device and is usually supported at its top end by one or more buoys, which support the weight of said line. In some cases, buoyancy units are also arranged along the riser. At its top end, the riser is connected to the jumper by a top connecting device, which can be of several forms.
In the prior art, top connecting devices are therefore known in which the riser is suspended below the buoy, the device being in the form of a gooseneck, said gooseneck being connected to both lines (riser and jumper) by flange-type connections with or without swivel joints. In this case, the buoy is connected to said device by a retaining element located between its bottom end and a support structure, which maintains and retains the ends of the two lines and the connection gooseneck. This type of connection is moreover described in patent FR 2 809 136 in combination with a catenary riser or in patent WO 02/103153 in combination with a vertical riser.
Another connecting device of the prior art involves making the connection at the top end of the buoy. Such a device is, in particular, described in U.S. Pat. No. 4,423,984, which shows a multiplicity of vertical risers surrounded by two buoys and connected to as many jumpers at the top end of the buoy.
However, these top connecting devices of the prior art do not give total satisfaction with regard to the many problems with which these devices are liable to be confronted. Some devices effectively involve long, costly installation procedures and do not, or only with difficulty, allow maintenance interventions of either standard or exceptional nature. For example, the top connecting device must effectively allow a smaller secondary line to be introduced into the riser for maintenance operations on subsea installations (so called “coiled tubing” operations) or introduction of tooling such as inspection “pigs”. In patent FR 2 809 136, this is performed using an element forming a secondary line as a retaining element between the buoy and the riser. In another case, “coiled tubing” is directly performed at the connecting device such as, for example, at the gooseneck, which features a section of bypass line providing direct secondary access to the riser.
Furthermore, the top connecting device must also allow replacement of the jumper, if need be, without requiring an excessively long production stoppage. Similarly, connection of the connecting device to the two lines must be simple and not complicate installation of the riser and the associated buoy.